Composite parts have become commonly used throughout industry because of their engineering qualities, design flexibility and low weight. In particular, honeycomb composite structures having a honeycomb core bonded between two composite face sheets provide excellent strength and stiffness to weight ratios that make them particularly valued and widely used in the aerospace industry. Generally, composite structures, such as honeycomb composite structures, are made up of multiple elements. And often, these elements intersect and are interconnected by adhesive that is applied at the interconnection of the elements and thereafter cured to permanently join the elements. In this regard, the integrity of the adhesive at the interconnection of the elements is typically critical to the performance of the structure. For example, in the aircraft industry, the quality of adhesive at the intersection of elements in composite spars and co-cured structures are critical to their performance. Flaws such as cracks, voids, or porosity can form in the adhesive and adversely affect the composite structure. In addition, flaws such as regions of inadequately cured adhesive can also adversely affect the composite structure.
To help ensure the integrity of adhesive interconnecting elements in composite structures, the adhesive is generally inspected for flaws. Such adhesive may not always be adequately inspected, however, particularly using traditional nondestructive inspection (NDI) methods. For example, one NDI method of inspecting adhesive joining elements of a composite structure includes using a hand-operated durometer that can measure the hardness near the surface of exposed adhesive. And while using a durometer to measure the hardness of the adhesive near the surface of the exposed adhesive can adequately detect flaws near the surface of the adhesive, many flaws exist well below the surface of the adhesive. Thus, such flaws are undetectable using conventional methods such as those utilizing a durometer.